SEOUL, March 17, 2011 (AFP) - South Korean pharmacists issued an appeal Thursday cautioning against panic over feared radiation exposure from Japan's quake-hit nuclear plants, as callers flooded drug stores with requests for iodide pills.

Fears over radiation spread through the Internet and text messages, prompting Seoul to launch a crackdown on scaremongering, as officials insisted that constant westerly winds will blow radiation out into the Pacific.

"Anxiety over radiation exposure is growing in this country following the explosion at Japan's nuclear power plants," the Korea Pharmaceutical Association said in a statement.

"Drug stores are being flooded with calls from people seeking to purchase iodine," it said.

The association said iodide tables could reduce the risk of thyroid cancer from radiation exposure but could also put users at risk of allergic reactions and problems with thyroid glands.

"As there is little possibility of radioactive dust reaching the country, heavy doses of iodide needed to fend off radiation impact would only bring about health hazards," it added.

Fears over radiation deepened on Thursday as Seoul started screening travellers from Japan and Japanese food for radiation.

Flights from Tokyo were fully booked as growing numbers of South Koreans joined the exodus, aviation companies said.

One Wednesday alone, some 6,000 passengers from Tokyo entered Seoul, up 30 percent from the usual number of travellers from Tokyo during weekdays.

South Korean police on Wednesday launched a crackdown on rumour mongerers spreading a false alarm through text messages and social networking sites that radioactive materials would soon reach the Korean peninsula.

The Financial Supervisory Service, Seoul's financial watchdog, also started a probe into a rumour doing the rounds in the financial markets which exacerbated a stock market plunge on Tuesday.

In South Korea, those who spread confusion by spreading false rumours can be jailed for up to one year.